/*
 * @(#)FirstApplicablePolicyAlg.java
 *
 * Copyright 2003-2005 Sun Microsystems, Inc. All Rights Reserved.
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 *      this list of conditions and the following disclaimer.
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 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
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package org.wso2.balana.combine.xacml2;

import org.wso2.balana.AbstractPolicy;
import org.wso2.balana.combine.PolicyCombinerElement;
import org.wso2.balana.combine.PolicyCombiningAlgorithm;
import org.wso2.balana.ctx.EvaluationCtx;
import org.wso2.balana.MatchResult;

import org.wso2.balana.ctx.ResultFactory;
import org.wso2.balana.ctx.AbstractResult;
import org.wso2.balana.ctx.xacml2.Result;

import java.net.URI;
import java.net.URISyntaxException;

import java.util.Iterator;
import java.util.List;

/**
 * This is the standard First Applicable policy combining algorithm. It looks
 * through the set of policies, finds the first one that applies, and returns
 * that evaluation result.
 * 
 * @since 1.0
 * @author Seth Proctor
 */
public class FirstApplicablePolicyAlg extends PolicyCombiningAlgorithm {

	/**
	 * The standard URN used to identify this algorithm
	 */
	public static final String algId = "urn:oasis:names:tc:xacml:1.0:policy-combining-algorithm:"
			+ "first-applicable";

	// a URI form of the identifier
	private static URI identifierURI;
	// exception if the URI was invalid, which should never be a problem
	private static RuntimeException earlyException;

	static {
		try {
			identifierURI = new URI(algId);
		} catch (URISyntaxException se) {
			earlyException = new IllegalArgumentException();
			earlyException.initCause(se);
		}
	}

	/**
	 * Standard constructor.
	 */
	public FirstApplicablePolicyAlg() {
		super(identifierURI);

		if (earlyException != null)
			throw earlyException;
	}

	/**
	 * Applies the combining rule to the set of policies based on the evaluation
	 * context.
	 * 
	 * @param context
	 *            the context from the request
	 * @param parameters
	 *            a (possibly empty) non-null <code>List</code> of
	 *            <code>CombinerParameter<code>s
	 * @param policyElements
	 *            the policies to combine
	 * 
	 * @return the result of running the combining algorithm
	 */
	public AbstractResult combine(EvaluationCtx context, List parameters,
			List policyElements) {
		Iterator it = policyElements.iterator();
		while (it.hasNext()) {
			AbstractPolicy policy = ((PolicyCombinerElement) (it.next()))
					.getPolicy();

			// make sure that the policy matches the context
			MatchResult match = policy.match(context);

			if (match.getResult() == MatchResult.INDETERMINATE)
				return ResultFactory.getFactory().getResult(
						AbstractResult.DECISION_INDETERMINATE,
						match.getStatus(), context);
			if (match.getResult() == MatchResult.MATCH) {
				// evaluate the policy
				AbstractResult result = policy.evaluate(context);
				int effect = result.getDecision();

				// in the case of PERMIT, DENY, or INDETERMINATE, we always
				// just return that result, so only on a rule that doesn't
				// apply do we keep going...
				if (effect != Result.DECISION_NOT_APPLICABLE
						&& !context.isSearching()) {
					return result;
				}
			}
		}
		// if we got here, then none of the rules applied
		return ResultFactory.getFactory().getResult(
				AbstractResult.DECISION_NOT_APPLICABLE, context);
	}

}
